1. Field of the Invention
The present invention relates to a control apparatus for a vehicular internal combustion engine, and particularly to a control apparatus for a vehicular internal combustion engine, which controls torque generated by an internal combustion engine by directly injecting fuel into a cylinder of the internal combustion engine.
2. Description of the Related Art
In recent years, in an internal combustion engine mounted in an automobile, in order to improve fuel consumption or the like, a direct-injection internal combustion engine in which fuel is directly injected into a combustion chamber of a cylinder by an injector is proposed and is put to practical use. In the direct-injection internal combustion engine, because of restrictions of pressure in a cylinder, a fuel injection period, a fuel atomization period and the like, fuel pressure is set to be higher than that of a conventional port injection internal combustion engine. The injector to inject the high pressure fuel has a large drive current and requires a drive circuit to control the large current.
In this type of conventional apparatus, an injector drive circuit is provided separately from an internal combustion engine control apparatus, an injector drive signal is transmitted from the internal combustion engine control apparatus to the injector drive circuit, and the, driving of the injector is controlled by the injector drive circuit in accordance with the injector drive signal. Besides, in accordance with a request for the practice of self diagnosis in an internal combustion engine control system, it is detected whether a drive current flows to an injector in synchronization with an injector drive signal, and failure of a fuel injection system is diagnosed based on the detection result (see, for example, patent document 1: JP-A-2000-73840 (pages 1 to 5, FIGS. 1 to 7).
In this conventional apparatus, in order to avoid such a problem that in a case where a signal line to transmit an abnormality diagnosis signal goes wrong (opened or shorted), although fuel injection can be normally carried out, it is judged that a fuel injection system goes wrong, and vehicle traveling is carelessly stopped, the internal combustion engine control apparatus detects the existence of a misfire at every cylinder, and in the case where the misfire is not detected although the abnormality diagnosis signal to indicate the abnormality of the fuel injection system is outputted, an energization signal to each cylinder is continuously outputted, and the fuel injection is continued.
However, according to the conventional apparatus as stated above, in the case where the abnormality of the fuel injection system is detected, and a fuel supply stop processing against the abnormality is carried out, since the judgment is made using the misfire judgment, in the case where the misfire judgment is carried out in a periodic measurement system, the reliability is low at the time of a period variation or in a low rotation region, and in the case where it is carried out in an ion detection system, an increase in cost is caused. Further, an increase in calculation load of the internal combustion engine control apparatus due to the misfire judgment processing is also conceivable.
Besides, the misfire is not necessarily generated by injector drive abnormality. In general, the connection from the injector drive circuit to the injector is such that the power supply side to the injector is common to group cylinders, and the GND side is independent in each cylinder. Thus, for example, in the case of a four-cylinder internal combustion engine having a first to a fourth cylinders, in the case where the ground (hereinafter referred to as GND) side harness of the third injector for the third cylinder is GND-shorted, since the power supply side is common to the second and the third injectors for the second and the third cylinders, at the time of driving the normal second injector, current flows to the third injector. Thus, the third injector is also driven at the same time as the second injector, and the second cylinder at the normal drive timing injects fuel, for example, in the intake stroke to cause normal combustion, while the third injector for the third cylinder injects fuel into the third cylinder in the expansion stroke. In the third cylinder, since the injection of the fuel occurs in the expansion stroke, a misfire signal is not detected, however, there arises a problem that the combustion is delayed, or the fuel flows out to the exhaust system.